In general, an LNG carrier is a vessel which stores LNG, which is obtained by liquefying natural gas to an ultra-low temperature in a gas field is stored, in an LNG storage tank and carries the stored LNG.
Examples of a propulsion system of the LNG carrier may include a steam turbine propulsion system using steam, a diesel engine propulsion system having a diesel engine for propulsion, and a dual fuel electricity propulsion system having a dual fuel engine, a generator, and a propulsion electromotor. The steam turbine propulsion system has low propulsion efficiency. Therefore, the diesel engine propulsion system or the dual fuel electricity propulsion system having high propulsion efficiency is mainly used as the propulsion system of the LNG carrier.
The LNG carrier, to which the diesel engine propulsion system is applied, includes a generation diesel engine and a generator which are separately installed therein, in order to supply electricity to electricity facilities inside the LNG carrier, that is, basic electricity facilities and cargo-related electricity facilities inside the LNG carrier.
In the case of the LNG carrier to which the dual fuel electricity propulsion system is applied, the dual fuel engine and the generator generate electricity and supply the generated electricity to electricity facilities inside the LNG carrier as well as the propulsion electromotor. In order to obtain the required electricity, an increased number of dual fuel engines and generators are installed and operated.
Meanwhile, an environment-friendly fuel cell may be adopted to generate electricity required in a vessel. The fuel cell obtains electricity through an electrochemical reaction of fuel-cell fuel, for example, hydrogen or synthetic gas having hydrogen. Conventionally, when the fuel-cell fuel is hydrogen, a hydrogen tank is installed in the vessel to store the hydrogen, and the stored hydrogen is supplied to the fuel cell from the hydrogen tank. However, since such a hydrogen tank has a limited size, the amount of hydrogen stored in the hydrogen tank may be limited.
Therefore, since the vessel including the conventional fuel cell has a limitation in supplying fuel-cell fuel, only fuel cells having a small capacity have been inevitably used as the conventional fuel cell, and the conventional fuel cell has been applied only to small vessels which sail a short distance. Furthermore, since the electricity generation capacity of the fuel cell is small, there is a limitation in using electricity generated by the fuel cell for electricity facilities inside the vessel. In particular, when the vessel having the conventional fuel cell operates a propulsion electromotor by using only the electricity generated from the fuel cell without including a separate generation engine, electromotors having a small output are inevitably used as the propulsion electromotor, because the electricity generation capacity of the fuel cell is small. Accordingly, since the speed of the vessel does not only decrease, but also most power is consumed by the propulsion electromotor, there is a larger limitation in using the electricity generated by the fuel cell for the electricity facilities inside the vessel.